trait CKEditor5ValidationTestTrait in Drupal 10

trait CKEditor5ValidationTestTrait {

  /**
   * Decorator for CKEditor5::validatePair() that returns an assertable array.
   *
   * @param \Drupal\editor\EditorInterface $text_editor
   *   The paired text editor to validate.
   * @param \Drupal\filter\FilterFormatInterface $text_format
   *   The paired text format to validate.
   * @param bool $all_compatibility_problems
   *   Only fundamental compatibility violations are returned unless TRUE.
   *
   * @return array
   *   An array with property paths as keys and violation messages as values.
   *
   * @see \Drupal\ckeditor5\Plugin\Editor\CKEditor5::validatePair
   */
  private function validatePairToViolationsArray(EditorInterface $text_editor, FilterFormatInterface $text_format, bool $all_compatibility_problems) : array {
    $violations = CKEditor5::validatePair($text_editor, $text_format, $all_compatibility_problems);
    $actual_violations = [];
    foreach ($violations as $violation) {
      if (!isset($actual_violations[$violation
        ->getPropertyPath()])) {
        $actual_violations[$violation
          ->getPropertyPath()] = (string) $violation
          ->getMessage();
      }
      else {

        // Transform value from string to array.
        if (is_string($actual_violations[$violation
          ->getPropertyPath()])) {
          $actual_violations[$violation
            ->getPropertyPath()] = (array) $actual_violations[$violation
            ->getPropertyPath()];
        }

        // And append.
        $actual_violations[$violation
          ->getPropertyPath()][] = (string) $violation
          ->getMessage();
      }
    }
    return $actual_violations;
  }

}